(function (doc, win) {
    var docEl = doc.documentElement,
        resizeEvt = "orientationchange" in window ? 'orientationchange' : 'resize',
        recalc = function () {
            var clientWidth = docEl.clientWidth;
            if (!clientWidth) return;

            docEl.style.fontSize = 20 * (clientWidth / 320) + 'px';
        };
    if (!doc.addEventListener) return;
    win.addEventListener(resizeEvt, recalc, false);
    doc.addEventListener("DOMContentLoaded", recalc, false)

})(document, window)